Gas engines generally include, as a combustion chamber, an auxiliary chamber, in addition to a main chamber. In the auxiliary chamber, an air-fuel mixture is ignited to produce a torch flame. The torch flame is injected to the main chamber to burn the air-fuel mixture in the main chamber. The air-fuel mixture supplied to the auxiliary chamber is richer than that supplied to the main chamber. The fuel gas is supplied to the auxiliary chamber through a supply path different from that for the main chamber. General configurations of such a gas engine are disclosed in Patent Documents 1 and 2, for example.
FIG. 5 is a diagram showing the relationship between an opening/closing timing of a feed/exhaust valve and the pressure in a cylinder, in the gas engine. In FIG. 5, main chamber solenoid valve open means that a main chamber solenoid valve for opening and closing a main chamber gas supply path, connecting between a fuel supply source and the main chamber, is opened. Similarly, auxiliary chamber solenoid valve open means that an auxiliary chamber solenoid valve for opening and closing an auxiliary chamber gas supply path, connecting between the fuel supply source and the auxiliary chamber, is opened.
As shown in FIG. 5, the period, during which the fuel gas can be supplied to the main chamber and the auxiliary chamber, is limited to a short period such as during an intake step, in which the pressure in the cylinder is low. The amount of fuel gas supplied to the auxiliary chamber is adjusted within the short period of time during which the auxiliary chamber solenoid valve is opened.
Patent Document 1: Japanese Patent Application Laid-open No. 2010-150983
Patent Document 2: Japanese Patent Application Laid-open No. 2010-265835